Polytrimethylene terephthalate composition particles and process for producing same

ABSTRACT

Poly(trimethylene terephthalate) composition particles comprising 80% by weight or more of trimethylene terephthalate units based on the entire repeating units, having an intrinsic viscosity from 0.8 to 2 dl/g, and satisfying the following conditions (a) to (c): (a) the composition particles have a particle size of 3 mm or less and a weight of less than 1 mg/particle; (b) the composition particles have a terminal carboxyl group content of 25 meq/kg or less; and (c) the composition particles have a cyclic dimer content of 1.5% by weight or less.

TECHNICAL FIELDS

The present invention relates to poly(trimethylene terephthalate)composition particles and a process for producing the same.

BACKGROUND ART

A poly(trimethylene terephthalate) (hereinafter abbreviated to PTT) is apolycondensation product of terephthalic acid and/or a lower alcoholester of terephthalic acid with 1,3-propane diol (also termedtrimethylene glycol, hereinafter abbreviated to PDO).

PTT fibers obtained by melt spinning a PTT have many excellentproperties such as an astonishingly soft feeling, drapability, excellentstretchability, low temperature dye-affinity and weathering resistance.Conventional synthetic fibers such as conventional poly(ethyleneterephthalate) (hereinafter abbreviated to PET) fibers and nylon 6fibers have no such excellent properties.

A process comprising once pelletizing a prepolymer of a PTT obtained bymelt polymerization, and heating the prepolymer in a pellet form withoutremelting the pellets to effect polymerization, namely, a productionprocess of a PTT in which melt polymerization is combined withsolid-state polymerization, has been known as a production process of aPTT.

Elementary reactions forming the polycondensation reactions of a PTTmainly include the following two types of reactions: the forwardreaction of a chain growth reaction (the following formula (a1)) inwhich PDO is removed from two terminal hydroxyl groups; the backwardreaction including a reaction (the following formula (a2), namely thereverse reaction of the formula (a1)) in which an ester portion isdecomposed with undischarged PDO and a thermal decomposition reaction(the following formula (b)).

A PTT is more likely to suffer a thermal decomposition reaction than aPET and a poly(butylene terephthalate) (hereinafter abbreviated to PBT),each having a skeleton similar to that of a PTT. That is, kd in theabove formula (b) is large. As a result, it is difficult to adequatelyincrease the molecular weight of a PTT by melt polymerization alone. Aprocess wherein solid-state polymerization (in which polymerization iscarried out at temperature as low as up to the melting point) is carriedout in combination is usually employed after melt polymerization.

However, various problems caused by the properties of the polymer arisein the production of a PTT.

A first problem is that a PTT tends to be thermally decomposed in a meltpolymerization step. Because kd is large in the above formula (b),lowering of the molecular weight of a PTT is likely to take place athigh temperature. Furthermore, carboxyl groups and allyl groups producedby thermal decomposition accelerate further thermal decomposition, whichcauses lowering of the whiteness and oxidation resistance stability ofthe polymer.

Inhibiting the thermal decomposition as much as possible thereforebecomes an essential requirement for obtaining a PTT of high quality inthe melt polymerization step of a PTT. However, known technologies arestill insufficient to satisfy the requirement. Such thermaldecomposition does not matter substantially in the production of a PETand a PBT. For a PET or a PBT, the thermal decomposition rate constantcorresponding to kd is far smaller in comparison with a PTT, and thethermal decomposition hardly takes place. As a result, polymers of highquality can be produced by melt polymerization alone, and polymers eachhaving a sufficiently high molecular weight can be obtained without acombination with solid-state polymerization. Accordingly, the firstproblem is one extremely specific to a PTT, and solution of the problemis difficult even when known information about a PET and a PBT is used.

A second problem is as follows: although solid-state polymerizationinhibits the thermal decomposition and a PTT having a high molecularweight can be obtained, the polymerization rate sometimes becomessignificantly low due to low polymerization temperature. It takes asignificantly long time for known technologies to subject a PTT tosolid-state polymerization, though the time differs depending on themolecular weight of a prepolymer and the molecular weight to beattained. A decrease in the productivity is therefore unavoidable.Moreover, although the polymerization temperature is low, thermaldecomposition of a polymer is unavoidable to a certain degree when thesolid-state polymerization is carried out at temperature close to 200°C. for a long period of time.

A third problem is as explained below. A PTT in a state of pellets tendsto be cracked, and powdery material is likely to be produced when PTTpellets rub together during transportation, drying, solid-statepolymerization, and the like of the PTT. Moreover, a cyclic oligomerformed during melt polymerization is contained in the PTT in a largeamount. When PTT pellets and the powdery material are in a mixture, yarnbreakage and fluff formation are likely to take place in themelt-molding step. Furthermore, because a cyclic oligomer is highlyvolatile, it is deposited around the spinning nozzle during the meltspinning step, and the deposits also cause yarn breakage and fluffformation.

The crack formation, generation of powdery material and deposition of acyclic oligomer are problems specific to a PTT. A PET and a PBT eachhaving a structure similar to a PTT substantially have no such problems.

When a PTT is produced by melt polymerization alone, the content of acyclic oligomer in the PTT amounts to 1.6 to 3.5% by weight. In contrastto the PTT, the oligomer content in a PET is about 1% by weight.Moreover, the oligomer of a PET is mostly cyclic trimer. However, thecyclic oligomer of a PTT is mostly cyclic dimer, and as a result thecyclic oligomer has a small molecular weight. The cyclic oligomer istherefore greatly volatile and soluble in water. Accordingly, theproblems of the cyclic oligomer in the production process of a PTT arefar more serious in comparison with those of a PET.

Several production processes in which melt polymerization andsolid-state polymerization are employed in combination have been known.However, no process that solves the above problems simultaneously hashitherto been known.

For example, Japanese Unexamined Patent Publication (Kokai) No. 8-311177describes that when PTT pellets are subjected to solid-statepolymerization at temperature close to 200° C. for a few hours invacuum, the oligomer content amounts to 1% by weight or less. However,the above problems except for the problem of the oligomer are notrecognized in the patent publication, and thus the patent publicationdoes not describe methods of solving the problems.

In the specification of U.S. Pat. No. 2001/0056172 A1, a process forsolid-state polymerizing PTT pellets in an amount from 10 to 15 mg isdescribed. However, generation of powdery material and the problem of acyclic oligomer are not recognized at all in the patent publication, andthus no suggestion related to methods for solving the problems isdescribed therein.

Japanese Unexamined Patent Publication (Kokai) No. 2000-159875 disclosesa process for obtaining a PTT of high grade by solid-state polymerizinga polymer obtained by melt polycondensing with a catalyst mixture of Tiand Mg in a specific state and having a low terminal vinyl groupcontent, under reduced pressure or in an inert gas atmosphere. However,because Mg is used as a catalyst in the process, the PTT has a dullcolor tone, and the L* value is as low as about 60 to 70; the pelletshave a poor color tone. Moreover, no suggestion about recognition of theabove problems or a method for solving the problems is describedtherein.

The pamphlet of International Patent WO 97/23543 describes a processcomprising dropping a molten PTT having a low polymerization degree on ahot plate without pelletizing, crystallizing the PTT at temperature from60 to 190° C. to form a PTT in a solid state having an apparent finecrystal size of 18 nm or more, and then solid-state polymerizing thePTT. However, the TTT obtained by the process has a drastically unevensurface, and easily produces powdery material when rubbed together. ThePTT is therefore estimated to have poor moldability. Moreover, thepamphlet includes no description about the color tone and improvement ofthe oxidation resistance stability, and neither describes nor suggestsrecognition of the problems about the moldability, crack formation andpowdery material of PTT or solution methods of the problems.

The pamphlet of International Patent WO 98/23662 describes in Example 8a process comprising pelletizing a PTT the terminals of which are sealedwith a hindered phenol stabilizer, and solid-state polymerizing thepelletized PTT. The pamphlet of International Patent WO 99/11709describes in Example 8 a process comprising pelletizing a PTT containinga phosphorus type stabilizer, and solid-state polymerizing thepelletized PTT. However, both pamphlets neither describe nor suggestrecognition of the problems about the moldability, crack formation andpowdery material of the PTT or solution of the problems.

DISCLOSURE OF THE INVENTION

The present inventors have carried out intensive investigations in orderto solve such problems specific to a PTT as explained above, namely, aproblem about lowering of whiteness of a PTT caused by the thermaldecomposition, a problem about the oxidation resistance stability, aproblem about low productivity of a PTT during the solid-statepolymerization step and a problem about lowering of the moldabilitycaused by the powdery material and cyclic dimer. As a result, thepresent inventors have found that a PTT can be polymerized even at lowtemperature at a markedly high solid-state polymerization rate by ratheractively utilizing the phenomenon that a PTT, which differs from a PETand a PBT, can be unusually easily powderized, and the cyclic dimercontent in the PTT can be decreased in comparison with PTT pellets, andthat fluff formation and yarn breakage are made to hardly take place ina melt molding step of a PTT that is not in pellets but in powder alonehaving a specific particle size.

Furthermore, the present inventors have also found that because a PTT isnot required to be polymerized to a high degree (high viscosity) in themelt-polycondensation step, the melt-polycondensation reaction can becarried out in a short period of time, and that a PTT having a highmolecular weight and having less suffered thermal decomposition to aminimum degree can be obtained even when the solid-state polymerizationis carried out at lower temperature.

A problem to be solved by the present invention is to provide PTTcomposition particles excellent in whiteness and oxidation resistancestability, showing yarn breakage and fluff formation to a decreaseddegree, and excellent in moldability. Specifically, an object of thepresent invention is to provide a process that comprises granulating areaction product obtained by melt-polycondensing a PTT, and subjectingthe granulated material to solid-state polymerization to give a PTT ofhigh quality having less suffered thermal decomposition, with highproductivity.

That is, the present invention is as explained below.

1. PTT composition particles comprising 80% by weight or more oftrimethylene terephthalate units based on the entire repeating units,having an intrinsic viscosity from 0.8 to 2 dl/g, and satisfying thefollowing conditions (a) to (c):

(a) the composition particles have a particle size of 3 mm or less and aweight of less than 1 mg/particle;

(b) the composition particles have a terminal carboxyl group content of25 meq/kg or less; and

(c) the composition particles have a cyclic dimer content of 1.5% byweight or less.

2. The PTT composition particles according to 1 mentioned above, whereinthe PTT composition particles have a cyclic dimer content of 2% byweight or less after maintaining the particles in a molten state at 260°C. for 30 minutes.

3. The PTT composition particles according to 1 or 2 mentioned above,wherein 95% or more of the particles pass through a 10-mesh filter, and5% or less of the particles pass through a 500-mesh filter.

4. PTT composition particles suited to solid-state polymerization,comprising 80% by weight or more of trimethylene terephthalate unitsbased on the entire repeating units, having an intrinsic viscosity from0.1 to 0.79 dl/g, and satisfying the following conditions (a) to (c):

(a) the composition particles have a particle size of 3 mm or less and aweight of less than 1 mg/particle;

(b) the composition particles have a terminal carboxyl group content of35 meq/kg or less; and

(c) the composition particles have a cyclic dimer content from 1.6 to3.5% by weight.

5. The PTT composition particles suited to solid-state polymerizationaccording to 4 mentioned above, wherein 95% or more of the particlespass through a 10-mesh filter, and 5% or less of the particles passthrough a 500-mesh filter.

6. A process for producing PTT composition particles comprising thefollowing steps (1) to (3):

(1) a step of reacting terephthalic acid and/or a lower alcohol esterderivative of terephthalic acid with 1,3-propanediol to form1,3-propanediol ester of terephthalic acid and/or a polymer thereof;

(2) a step of granulating 1,3-propanediol ester of terephthalic acidand/or a polymer thereof obtained in the step (1); and

(3) a step of heating granulated 1,3-propnanediol ester of terephthalicacid and/or a polymer thereof in a solid-state, whereby the intrinsicviscosity is increased by 0.1 dl/g or more.

7. The process for producing PTT composition particles according to 6mentioned above, wherein the method of granulating 1,3-propanediol esterof terephthalic acid and/or a polymer thereof is at least one of thefollowing methods (1) to (3):

(1) a method comprising extruding the ester and/or the polymer in amolten state, and then cutting the extruded material;

(2) a method comprising atomizing the ester and/or the polymer in foggystate, and then finely granulating the atomized material; and

(3) a method comprising solidifying the ester and/or the polymer, andthen crushing the solidified material.

8. The process for producing PTT composition particles according to 6 or7 mentioned above, wherein the particle size is 3 mm or less, and theparticle weight is less than 1 mg/particle.

9. The process for producing PTT composition particles according to 7mentioned above, wherein 95% or more of the particles pass through a10-mesh filter, and 5% or less of the particles pass through a 500-meshfilter.

10. The process for producing PTT composition particles according to anyone of 6 to 9 mentioned above, wherein the composition particles have aterminal carboxyl group content originating from the polymer of1,3-propanediol ester of terephthalic acid of 35 meq/kg or less.

11. A process for producing PTT composition particles comprising heatingthe PTT composition particles according to 3 or 4 mentioned above in asolid-state to increase the intrinsic viscosity by 0.1 dl/g or more.

12. The process for producing PTT composition particles according to anyone of 6 to 11 mentioned above, wherein the PTT composition particlesare heated in a solid-state to increase the intrinsic viscosity by 0.1dl/g or more, and part of or the entire of the polycondensation activityremaining in the catalyst is deactivated.

13. The process for producing PTT composition particles according to 12mentioned above, wherein the method of deactivating part of or theentire of the polycondensation activity of the catalyst is a methodcomprising contacting the particles with a polar compound having atemperature of 50° C. or above.

14. A process for producing PTT composition particles comprisingcontacting the PTT composition particles according to any one of 1 to 3mentioned above with a polar compound having a temperature of 50° C. orabove.

15. The process for producing PTT composition particles according to 13or 14 mentioned above, wherein the polar compound is at least onesubstance selected from the group consisting of water, methanol,phosphoric acid, hydrogen chloride, sulfuric acid and ammonia.

16. A molded article prepared by molding the PTT composition particlesaccording to any one of 1 to 3 mentioned above.

17. A fiber prepared by molding the PTT composition particles accordingto any one of 1 to 3 mentioned above.

18. A tire cord prepared by molding PTT composition particles comprising80% by weight or more of trimethylene terephthalate units based on theentire repeating units, and having an intrinsic viscosity from 0.8 to 2dl/g.

19. A tire for which a tire cord according to 18 mentioned above isused.

The present invention is explained below in detail.

A PTT forming the PTT composition particles of the present invention isa polymer comprising 80% by weight or more of trimethylene terephthalateunits based on the entire repeating units. The PTT may therefore becopolymerized with a comonomer other than terephthalic acid and PDO inan amount of 20% by weight or less, preferably 10% by weight or lessbased on the entire repeating units.

Examples of the comonomer include oxalic acid, succinic acid, adipicacid, sebacic acid, dodecanoic acid, dodecanoic diacid,cyclohexanedicarboxylic acid, 5-sodiumsulfoisophthalic acid, ethyleneglycol, butanediol, hexanediol, cyclohexanediol, cyclohexanedimethanol,trimethylene glycol dimer and a polyalkylene glycol having an averagemolecular weight from 400 to 20,000. These compounds may be used singly,or at least two of them may be used in combination.

The PTT composition particles of the present invention may optionallycontain various additives such as delustering agents, thermalstabilizers, defoaming agents, color modifying agents, flame retardants,antioxidants, UV-ray absorbers, IR-ray absorbers, crystallizationnucleating agents and fluorescent brighteners. These additives may becopolycondensed or mixed. Titanium oxide is preferred as the delusteringagent, and the content is preferably from 0.01 to 3% by weight based onthe PTT composition particles.

Furthermore, in order to inhibit thermal decomposition during thepolymerization step, a thermal stabilizer is preferably used. Examplesof the thermal stabilizer include phosphorus compounds such asphosphoric acid, trimethyl phosphate and triethyl phosphate. A thermalstabilizer, for example, a phosphorus compound is used in a content ofpreferably from 2 to 250 ppm, and more preferably from 10 to 100 ppm asphosphorus based on the PTT composition particles. A hindered phenoltype antioxidant may also be used as the thermal stabilizer in an amountof 0.01 to 1% by weight based on the PTT composition particles.

When the PTT composition particles are colored, a color modifying agentsuch as cobalt acetate, cobalt formate and a fluorescent brightener mayalso be added in an amount from 0.0001 to 0.05% by weight based on thePTT composition particles.

The intrinsic viscosity of the PTT composition particles of the presentinvention is from 0.8 to 2 dl/g, preferably from 0.8 to 1.5 dl/g.

When the intrinsic viscosity is less than 0.8 dl/g, the polymerizationdegree becomes low. As a result, the strength and durability of themolded article after melt molding decrease. Moreover, when the intrinsicviscosity exceeds 2 dl/g, the melt viscosity becomes excessively high,and the melt spinning becomes difficult.

In view of the solid-state polymerization rate and moldability, theparticle size of the PTT composition particles of the invention is 3 mmor less, and the particle weight is less than 1 mg/particle.

When the particle size exceeds 3 mm, the solid-state polymerization ratebecomes slow, and powder is generated during drying, transportation,solid-state polymerization, or the like, to cause lowering of themoldability. Although there is no specific limitation on the lower limitof the particle size, the lower limit is about 0.01 μm that is a minimumvalue attainable by conventional powderizing technologies.

In view of the easiness of granulation and post-treatment of the PTTcomposition particles with polar material, the particle size ispreferably from 2.7 mm to 1 μm, and most preferably from 2 mm to 25 μm.

In addition, the size of a PTT composition particle designates thelongest portion of the particle. For example, when the particle isapproximately circular, the particle size designates the diameter, andwhen the particle is approximately elliptical, the particle sizedesignates the major axis.

Furthermore, the PTT composition particles of the invention arepreferably particles 95% or more of which pass through 10-mesh filter,and 5% or less of which pass through a 500-mesh filter. The particlesparticularly preferably pass through a 10-mesh filter in an amount of97% or more, and a 500-mesh filter in an amount of 3% or less. Whenamounts of particles that pass through the above filters are in theabove ranges, PTT composition particles having uniform quality withrespect to a polymerization degree, whiteness, a cyclic dimer content,and the like, are obtained. PTT composition particles being uniform, andhaving a uniform particle size and a fine particle shape showsignificant heat transfer effects, and can be dried in a short period oftime and extruded at low temperature. The particles therefore showmarked effects of inhibiting thermal deterioration, and the like.

In view of the moldability, the weight of PTT composition particles isless than 1 mg/particle, preferably 0.5 mg/particle or less, and morepreferably 0.3 mg/particle or less. When the particles have anexcessively small weight, they are likely to aggregate. The lower limitof the weight is preferably 0.0001 mg/particle or more from thestandpoint of inhibiting the aggregation.

The PTT composition particles of the invention have a content ofcarboxyl groups situated at the PTT molecular ends of 25 meq or less perkg of the PTT composition particles, preferably 15 meq/kg or less, andmore preferably 12 meq/kg or less. When the terminal carboxyl groupcontent exceeds 25 meq/kg, the particles are colored during heating, andthe oxidation resistance stability is lowered.

The PTT composition particles of the present invention have a cyclicdimer content of 1.5% by weight or less based on the weight of the PTTcomposition particles, preferably 1.3% by weight or less, and morepreferably 1% by weight or less. When the cyclic dimer content is in theabove range, cyclic dimer causes no problem during the spinning andprocessing steps. In addition, a smaller content of cyclic dimer ispreferred, and a cyclic dimer content of zero is most preferred.

Cyclic dimer is a substance having a structure of the formula (1):

wherein Ph is a benzene ring originating from terephthalic acid.

The PTT composition particles of the invention having been maintained ina molten state at 260° C. for 30 minutes has a cyclic dimer content ofpreferably 2% by weight or less, more preferably 1.8% by weight or less,still more preferably 1.5% by weight or less, and particularlypreferably 1.1% by weight or less. When PTT resin composition particleshaving a cyclic dimer content of 2% by weight or less are remelted andthe molten material is subjected to melt molding such as melt spinning,melt filming, injection molding, extrusion molding or blow molding, anincrease in the amount of cyclic dimer can be markedly decreased. Inaddition, there is no specific limitation to the lower limit of thecyclic dimer content. A smaller cyclic dimer content is preferred, and acyclic dimer content of zero is most preferred.

The PTT composition particles of the present invention preferably showan L* value of 75 or more, and a b* value from −2 to 5.

When the PTT composition particles showing an L* value of 75 or more, ora b* value or 5 or less are colored with, for example, a dye or apigment, the products obtained therefrom are excellent in color tone andbrightness. In order to obtain more excellent color development andbrightness of the products, the L* value is preferably 80 or more, andmore preferably 85 or more, and the b* value is preferably from −1 to 5,and more preferably from −1 to 4.

In addition, the L* value and the b* value are indexes of color tonerepresented by the CIE-L*a*b* (CIE 1976) color system. The L* valuerepresents brightness. A larger L* value signifies that the color toneis brighter. The b* value represents yellowness, and a larger b* valuesignifies that the yellowness becomes stronger.

One preferred example of a process for producing PTT compositionparticles of the invention is explained below.

The PTT composition particles of the invention are produced by thefollowing steps: (1) a condensation step of reacting terephthalic acidand/or a lower alcohol ester of terephthalic acid with PDO to formbis(3-hydroxypropyl) terephthalate and/or a polymer thereof; (2) a stepof granulating bis(3-hydroxypropyl) terephthalate and/or a polymerthereof thus obtained; and (3) a step of subjecting the particles thusobtained to solid-state polymerization.

A polymer of bis(3-hydroxypropyl) terephthalate herein is a polymer inwhich trimethylene terephthalate units are connected. The polymerizationdegree is preferably 2 or more, and more preferably from 3 to 100.Hydroxyl groups, carboxyl groups, allyl groups, and the like may bepresent at the molecular ends.

First, the polycondensation step (1) is explained below.

For polymerization starting materials, the charging ratio of PDO toterephthalic acid and/or a lower alcohol ester of terephthalic acid ispreferably from 1 to 3 in terms of a molecular ratio, more preferablyfrom 1.4 to 2.5, and still more preferably from 1.5 to 2.3. When thecharging ratio is in the above range, the esterification reactionproceeds smoothly, and a polymer having a high melting point andexcellent in whiteness is obtained.

Furthermore, a lower alcohol ester of terephthalic acid is preferred asa starting material because the PTT composition particles thus obtainedhave a good color tone.

In order to make the reaction proceed smoothly, use of a catalyst ispreferred. Examples of the catalyst include titanium alkoxides such astitanium tetrabutoxide and titanium tetraisopropoxide, metal oxides suchas amorphous titanium oxide precipitates, amorphous titaniumoxide/silica coprecipitates and amorphous zirconia precipitates, metalcarboxylates such as calcium acetate, manganese acetate, cobalt acetateand antimony acetate and germanium compounds such as germanium dioxide.Use of the catalyst in an amount from 0.01 to 0.2% by weight based onthe entire carboxylic acid component monomer is preferred in view of thereaction rate and the polymer whiteness.

The reaction temperature is preferably from about 200 to 250° C. Thereaction can be carried out while by-produced water and an alcohol suchas methanol are being distilled off. The reaction time is usually from 2to 10 hours, and preferably from 2 to 4 hours.

The reaction products thus obtained are bis(3-hydroxypropyl)terephthalate and/or an oligomer thereof. The polycondensation reactionmay also be made to proceed further in a molten state.

An object of the polycondensation reaction is to make the polymer havesuch a molecular weight that the polymer is solid at solid-statepolymerization temperature from 190 to 225° C. That is, the object is tomake the polymer have a melting point higher than 190° C. It is notnecessary to drastically increase the molecular weight.

In the polycondensation reaction, the following materials may optionallybe added further: titanium alkoxides such as titanium tetrabutoxide andtitanium tetraisopropoxide, metal oxides such as amorphous titaniumoxide precipitates, amorphous titanium oxide/silica coprecipitates andamorphous zirconia precipitates, and germanium compounds such asgermanium dioxide. The materials may be added in an amount from 0.01 to0.2% by weight based on the entire carboxylic acid component monomers,and the polycondensation may be carried out according to a known method.

The polycondensation reaction is carried out at temperature preferablyfrom 240 to 270° C. and more preferably from 250 to 265° C., at a vacuumdegree preferably from 0.0001 to 1 kPa for an optimum polymerizationtime that is usually 3 hours or less, and preferably from 0.3 to 2hours, while the terminal carboxylic acid content of the reactionproduct is being evaluated; the reaction is carried out so that theterminal carboxylic acid content becomes 35 meq/kg or less.

Furthermore, in order to efficiently distill PDO off during thepolycondensation reaction, it is important to increase the surface areaof the polymer. In order to increase the surface area, for example, ahelical stirring apparatus, a disc ring reactor, or the like isemployed, and efficient stirring is conducted so that the reactionproduct is raked up to form a film. At the same time, the charging ratioof the starting material based on the volume of the polycondensationreactor is set at preferably 40% or less, more preferably 35% or less.

Furthermore, it is preferred to stop the polycondensation reaction whilethe viscosity of the molten material in the polycondensation reactionstep is increasing with time. It is important to finish thepolycondensation reaction before the viscosity thereof stops to increasewith time or rather decreases, for the following reasons. When theviscosity does not increase with time or rather decreases, the thermaldecomposition reaction becomes predominant over the polycondensationreaction, and the content of terminal carboxylic acid formed by thermaldecomposition increases.

In addition, phosphorus compounds mentioned above, hindered phenolantioxidants and color modifying agents can be added at an optional stepof the polycondensation reaction, preferably prior thereto.

The intrinsic viscosity of the reaction product obtained through thepolycondensation reaction is usually from 0.1 to 0.79 dl/g; it ispreferably from 0.1 to 0.5 dl/g in order to inhibit thermaldecomposition. Moreover, the resultant polymer contains cyclic dimerusually in an amount from 1.6 to 3.5% by weight.

When the polycondensation step is completed, the granulating step (2) issubsequently carried out.

There is no specific limitation on the method for granulating1,3-propanediol ester of terephthalic acid (namely, bis(3-hydroxypropyl)terephthalate) and/or a polymer thereof taken out of thepolycondensation reactor. However, examples of the method include thefollowing ones: a method comprising extruding the ester and/or a polymerthereof in a molten state, preferably cooling the extruded material tobe solidified, and finely cutting the extruded material; a methodcomprising atomizing the ester and/or a polymer thereof in a foggystate, and cooling the atomized material to form fine particles; and amethod comprising solidifying the ester and/or a polymer thereof, andcrushing the solidified material.

Known methods for crushing can be employed. Apparatuses such as aHenschel mixer, a ball mill and a crusher can be used for crushing. Theparticle size and the particle weight of the particles thus obtained areas described above.

The prepolymer composition thus obtained in a particle form is subjectedto solid-state polymerization (3) to give the PTT composition particlesof the present invention.

Next, a method for producing PTT composition particles of the presentinvention from the prepolymer composition in a particle form isexplained below.

In addition, solid-state polymerization herein signifies to increase anintrinsic viscosity of the prepolymer composition by 0.1 dl/g or more byheating the composition in a solid state.

Prior to solid-state polymerization, the prepolymer composition ispreferably crystallized by heat treating the composition at temperatureof the melting point or below. The crystallization can suppressvariation in the extraction rate caused by melt sticking of particlesduring the solid-state polymerization.

When the polycondensation is conducted, the crystallization is carriedout under the following heat treatment conditions: preferably in aninert gas atmosphere at temperature that the particles attain from 190to 225° C. preferably for a time from 5 to 120 minutes. When thetemperature is in the above range, crystallization proceeds sufficientlyto produce no nonuniform crystal formation. As a result, no meltsticking of the particles takes place during the solid-statepolymerization.

In addition, when nonuniform polymerization is produced in theprepolymer by drastic heat treatment of the prepolymer, heat treatmentof the prepolymer at temperature from 80 to 180° C. for 5 to 120 minutesprior to the crystallization heat treatment is preferred.

Furthermore, when the polycondensation step is omitted, a method ofgradually heating the prepolymer to temperature from 100 to 200° C. ispreferred as crystallization heat treatment, because melt sticking andmelting of the prepolymer is avoided. In the crystallization stage,increasing the molecular weight and discharging by-products such as PDOmay also be conducted.

In order to inhibit coloring of a PTT in the solid-state polymerization,and increase the solid-state polymerization rate, the solid-statepolymerization temperature is preferably from 170 to 225° C., morepreferably from 190 to 215° C., and most preferably from 195 to 210° C.When the solid-state polymerization temperature is in the above range,the following advantages are obtained: a sufficient solid-statepolymerization rate is obtained; no thermal decomposition of the PTTtakes place; no PTT particles melt stick to the wall surface of thesolid-state polymerizer; and the PTT is not highly polymerized, and ahighly crystallized product is not formed. As a result, melt stabilityof the PTT is obtained during spinning and molding.

The solid-state polymerization is carried out in a vacuum atmosphere orunder an inert gas stream. Both procedures are effective in efficientlydischarging polymerization by-products such as water and PDO from theparticle surfaces; it is important to carry out the solid-statepolymerization under specific polymerization conditions.

When solid-state polymerization is carried out in a vacuum atmosphere,the polymerization is carried out under pressure of preferably 30 kPa orless, more preferably 20 kPa or less, and most preferably from 0.001 to10 kPa for the purpose of efficiently discharging polymerizationby-products.

Procedures of carrying out solid-state polymerization under an inert gasstream are explained below.

The inert gas herein designates a gas that does not react with a PTTsubstantially at solid-state polymerization temperature. Examples of theinert gas include nitrogen, argon and neon. Use of nitrogen gas ispreferred in view of cost. When the inert gas contains oxygen, thermaldecomposition of the PTT is promoted during solid-state polymerization,and the PTT is colored. The oxygen content is therefore preferably 100ppm or less based on the inert gas.

The solid-state polymerization is carried out while inert gas is allowedto flow into a solid-state polymerizer in which granular PTT has beenplaced. A superficial velocity that is a flow rate of the inert gas atthe time is preferably 2 cm/min or more in view of the solid-statepolymerization rate. Although there is no specific limitation on theupper limit of the superficial velocity, the upper limit is preferably400 cm/min to avoid wasting the inert gas because the efficiency ofdischarging polymerization by-products is not further improved when thesuperficial velocity exceeds 400 cm/min.

In addition, the superficial velocity is a value obtained by dividing agas flow rate (cm³/min) by a cross-sectional area (cm²) of thesolid-state polymerizer through which the gas passes.

Examples of the method for allowing inert gas to flow include a methodcomprising continuously feeding a granular prepolymer composition at aconstant rate to one side of a solid-state polymerizer, allowing aninert gas to flow in the direction reverse to the flow of the granularprepolymer composition, and continuously extracting the resultantproduct at a rate equal to the feeding rate of the granular prepolymercomposition from the other side thereof, and a method comprising placingthe granular prepolymer composition in a solid-state polymerizer,preferably with the contents stirred, and allowing an inert gas to flowat a superficial velocity as mentioned above.

A solid-state polymerizer is satisfactory as long as granular prepolymercomposition can be heated from the inner wall thereof. For example, thefollowing polymerizer is preferred: a banker type polymerizer wherein aninlet of a granular prepolymer composition is provided to the upperportion of a cylindrical tube, a conical outlet is provided at the lowerportion thereof, and heat is provided to the polymerizer from theoutside with a heating medium or steam.

The residence time of a granular prepolymer composition within thesolid-state polymerizer is preferably from 0.5 to 20 hours, and morepreferably from 0.5 to 10 hours. Continuous solid-state polymerizationis preferred due to the high productivity compared with that of batchtype solid-state polymerization in which the PTT is processed batchwise.

In order to carry out discharging PDO efficiently in the solid-statepolymerization, it is preferred to efficiently stir or fluidize thegranular prepolymer composition.

The solid-state polymerization as explained above makes the PTT have ahigh molecular weight and a decreased cyclic dimer content.

Moreover, although the PTT composition particles thus obtained areexcellent in whiteness, oxidation resistance stability and moldability,they are preferably treated with a polar compound. When a catalyst isused in the polycondensation step, the PTT composition particlessubsequent to solid-state polymerization contain a catalyst forpolycondensing a polymer of 1,3-propanediol ester of terephthalic acid.Part of or the entire polycondensation activity of the catalyst can bedeactivated by treating the particles with a polar compound.Deactivation of the catalyst inhibits an increase in cyclic dimer duringmelting in the molding step, and more preferable PTT compositionparticles having excellent light resistance are obtained.

Because the PTT composition particles in the present invention have alarge specific surface area, the above treatment of the particles with apolar compound can be carried out efficiently in comparison withtreatment of pellets.

Although there is no specific limitation on the procedure for contactingthe PTT composition particles with a polar compound, the treatment witha polar compound is satisfactory as long as partial or completedeactivation of the catalyst is observed when the treatment is carriedout. Examples of the procedure include a procedure in which the PTTcomposition particles are placed in a polar compound atmosphere, and aprocedure in which a polar compound is injected or placed in the PTTcomposition particles that are in a molten state, a solid state, asolution state or a dispersed state.

The temperature at which the PTT composition particles are treated witha polar compound is preferably 50° C. or above, more preferably 70° C.or above, still more preferably 150° C. or above, and most preferablyfrom 180 to 220° C.

During the treatment, the polar compound may be a liquid, a gas or afluid that is at a critical point or above.

Although there is no specific restriction on the treatment time,solvolysis of the PTT takes place more, and the molecular weight lowersmore when the treatment time increases. It is therefore preferred totreat the PTT in as short a period of time as possible. The treatmenttime is preferably 60 minutes or less usually, more preferably 30minutes or less, and still more preferably 10 minutes or less.

The polar compound is a compound having a heteroatom such as oxygen,nitrogen, phosphorus and sulfur, and more preferably is a compoundcapable of forming a hydrogen bond. Specific examples of such a compoundinclude water, alcohols such as methanol, ethanol, propanol, PDO,1,4-butanediol, ethylene glycol, glycerin and ethanolamine, phosphoruscompounds such as trimethyl phosphate, triethyl phosphate, tributylphosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite,triphenyl phosphite, phosphoric acid and phosphorous acid, acids such asformic acid, acetic acid, propionic acid, hydrogen chloride and sulfuricacid, and amines such as ammonia, methylamine, dimethylamine,ethylenediamine, triethylamine, ethyleneimine and amine. Of thesecompounds, water, methanol, phosphoric acid, hydrogen chloride, sulfuricacid and ammonia are preferred, and water is particularly preferredbecause water is easy to handling and has nontoxic properties.

There is no specific restriction on the ratio of a polar compound to PTTcomposition particles of the invention when both materials are contactedwith each other. A weight ratio from 100,000/1 to 0.01/1 is usuallysatisfactory.

Because the PTT composition particles of the invention thus obtained areexcellent in whiteness, oxidation resistance stability and moldability,the particles can be processed to give molded material such as fibers,films and molded articles by known procedures such as melt molding andwet molding.

Because the fibers are particularly excellent in a soft feeling, fatigueresistance and elastic recovery, the fibers are useful for clothing andindustrial material applications. Examples of the form of the fibersinclude multifilaments, a monofilament, staple fibers and nonwovenfabrics. The single filament size may be from 0.0001 to 30,000 dtex, andthe total filament size may be from 5 to 30,000 dtex. Moreover, theintrinsic viscosity is preferably from 0.8 to 2 dl/g in view of thefatigue resistance. The strength is preferably 3 cN/dtex or more, andmore preferably 4 cN/dtex or more. The elongation is preferably from 10to 50%.

Examples of an appropriate application of the fibers include anapplication of the fibers to reinforcing materials for tires, belts,hoses, and the like, wherein the fibers are used as a twisted yarnproduct (twisted yarn cord). In particular, the fibers are extremelyuseful as tire cords for bias tires in which the excellent oxidationstability resistance and fatigue resistance are utilized. There is nospecific limitation on the type of a twisted yarn, the method oftwisting and the number of doubled and twisted yarns. Examples of thetypes of twisted yarns include a single twist yarn, a plied yarn, aplied yarn of different nature of strand and a hard twisted yarn. Thereis no specific restriction on the number of doubled and twisted yarns.Examples of the twisted yarns include one twisted yarn, two twistedyarns, three twisted yarns, four twisted yarns and five twisted yarns.At least six doubled and twisted yarns may also be used. Yarns otherthan the PTT yarns such as nylon yarns, PET yarns, aramid yarns or rayoncan be used in combination with PTT yarns for the doubled and twistedyarns.

There is no specific limitation on the number of twist, and the numbercan be suitably selected while the single filament size and the totalsize are taken into consideration. The number of twist may be optionallyselected in accordance with texturing conditions and the environment inwhich the fibers are used. For example, for a twisted yarn cord formedout of multifilaments having a single filament size from 0.01 to 10dtex, and a total size from 30 to 100,000 dtex, a twisted yarn cordhaving a twist factor K (T/m·dtex^(0.5)) represented by the followingformula of 1,000 to 30,000 is preferred in view of the fatigueresistance and the manifestation of the strength:K=Y×D ^(0.5)wherein Y is a number of twist (T/m) per meter of the twisted yarn cord,and D is a total size (dtex) of the twisted yarn cord. The total sizeherein is a sum of the size of the entire yarns used for the twistedyarns. For example, when three yarns each having a size of 1,660 dtexare twisted, the total nominal size of the twisted yarn product becomes4,980 dtex (1,660×3). When a plurality of yarns are twisted andsubjected to multiple twist such as first twist and second twist, thenumber of twist to which the yarns are finally subjected is defined as atwist number Y, and the twist factor is calculated.

A solution containing 10 to 30% by weight of resorcin-formalin-latex(hereinafter abbreviated to RFL) is allowed to adhere to such a twistedyarn cord, and the twisted yarn cord is heated to 100° C. or above,whereby the twisted yarn cord is coated therewith. A treated cordexcellent in thermal properties can thus be obtained. An amount ofadhesion of the RFL resin is preferably from 2 to 7% by weight based onthe yarn weight.

There is no specific limitation on the composition of an RFL solution.An RFL solution the composition of which has been known can be usedwithout further processing or with modification. A preferred compositionof an RFL solution is as follows: 0.1 to 10% by weight of resorcin, 0.1to 10% by weight of formalin, and 1 to 28% by weight of latex. A morepreferred composition thereof is as follows: 0.5 to 3% by weight ofresorcin, 0.5 to 3% by weight of formalin, and 10 to 25% by weight oflatex.

In the treatment with an RFL solution, the drying temperature ispreferably from 120 to 250° C. and more preferably from 130 to 200° C.,and the drying time is 10 sec or more, and preferably from 20 to 120sec. Moreover, the RFL-coated cord subsequent to drying is thendesirably subjected to constant-length heat treatment. For the heattreatment conditions, the heat treatment temperature is preferably themaximum thermal shrinkage temperature ±50° C., more preferably themaximum thermal shrinkage temperature ±10° C., and most preferably themaximum heat shrinkage temperature ±5° C. The heat treatment time ispreferably from 10 to 300 sec, and more preferably from 30 to 120 sec.Moreover, during the heat treatment, the cord is desirably maintained ata constant length. The dimensional change subsequent to the heattreatment is preferably 3% or less, more preferably 1% or less, and mostpreferably 0%.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be further explained below by makingreference to examples. However, needless to say, the present inventionis in no way restricted thereto.

In addition, methods of measurements, methods of evaluation, and thelike are as explained below.

(1) Intrinsic Viscosity

Using an Ostwald viscometer, the ratio (η_(sp)/C) of a specificviscosity η_(sp) to a concentration C in terms of g/100 ml of a samplein o-chlorophenol at 35° C. is determined. The ratio (η_(sp)/C) isextrapolated to zero concentration. The intrinsic viscosity [η] isobtained from the following formula:[η]=lim (η_(sp) /C)C→0

(2) Particle Size and Particle weight

The length of the longest portion of each of freely optionally selected50 PTT composition particles is measured with calipers and a microscope,and the average of the measured values is defined as the particle size.

Moreover, the average weight of optionally selected 50 PTT compositionparticles is determined, and defined as the particle weight.

(3) Amount of Particles That Pass through Filter

PTT composition particles in an amount of 50 g are allowed to passthrough a 10-mesh (opening size of 1.70 mm as specified by JIS Z 8801).Moreover, the same procedure is conducted using a 500-mesh (opening sizeof 25 μm as specified by JIS Z 8801) filter. The amount (%) of the PTTcomposition particles that have passed through the 10-mesh filter andthe amount (%) of the PTT composition particles that have passed throughthe 500-mesh filter are respectively determined.

(4) Terminal Carboxyl Group Content

PTT composition particles in an amount of 1 g are dissolved in 25 ml ofbenzyl alcohol, and 25 ml of chloroform is added to the solution. Thesolution is titrated with a 1/50 N solution of KOH in benzyl alcohol.The terminal carboxyl group content per kg of particles (meq/kg) isdetermined from the following formula:terminal carboxyl group content=(VA−V0)×20  (2)wherein VA is a titrated amount (ml) thus obtained, and V0 is a titratedamount obtained without PTT composition particles (blank titration).

(5) Content of Cyclic Dimer

A sample in an amount of 0.3 g is dissolved in a mixture solution of 5ml of chloroform and 5 ml of (CF₃)₂CHOH, and 5 ml of chloroform isfurther added, followed by adding about 80 ml of acetonitrile. Theundissolved material then precipitated is separated by filtration, andall the filtrates are collected. Acetonitrile is added to the solutionso that the resultant solution has a volume of 200 ml.

The solution is analyzed with high performance liquid chromatography todetermine an amount of cyclic oligomer. The column used is μ Bondasphere C-18-100A column (size of 15 μm, 3.9 mm×150 mm) manufactured byWaters Corporation Inc. Water/acetonitrile (volume ratio of 30/70) isused as the mobile phase, and a UV-ray having a wavelength of 242 nm isused as the detector. The analysis is carried out at 45° C. at a flowrate of 1.5 ml/min.

(6) Color Tone (L*, b*)

A glass-made cell (an inside diameter of 61 mm and a depth of 30 mm) isfilled with PTT composition particles to the depth from 90 to 100% ofthe depth of the cell. L* and b* in the CIE-L*a*b* (CIE 1976) colorsystem of the sample are measured with a color difference meter (tradename of SM-7-CH, manufactured by SUGA TEST INSTRUMENTS CO., LTD.).

(7) Oxidation Resistance Stability

PTT composition particles are heated in the air at 220° C. for 24 hours,and the b* value is determined and used as an index of oxidationresistance stability.

(8) Melting Test of PTT Composition Particles at 260° C.

A sample in an amount of 1 g is placed in a glass ample, which isevacuated, and sealed therein by melting. The glass ample is placed inan oil bath at 260° C., and heated for 30 minutes. The glass ample isthen taken out, and cooled. The sample is taken out, and the cyclicdimer content of the sample is determined.

EXAMPLE 1 to 3

Dimethyl terephthalate in an amount of 1,300 g (6.7 moles), 1,144 g (15moles) of PDO and 0.78 g of titanium butoxide were charged into a3-liter autoclave equipped with plate-like blades. A transesterificationreaction was carried out at 220° C. while methanol was being distilledoff. The transesterification reaction ratio was 95%. After finishing thetransesterification reaction, 0.52 g of titanium tetrabutoxide as acatalyst and 0.65 g of trimethyl phosphate as a thermal stabilizer wereadded to the reaction mixture, and the contents were stirred for 30minutes. A polycondensation reaction was carried out for 2 hours at 260°C. at a vacuum degree of 20 Pa while PDO was being distilled off. Afterthe reaction, the polymer thus obtained was extruded in a rope-like formfrom the bottom portion of the polycondensation reaction reactor. Therope-like polymer was cut to give pellets having an intrinsic viscosityof 0.5 dl/g and a weight of 25 mg/pellet.

The pellets thus obtained were placed in a sample mill (trade name ofSM-1, manufactured by Iuchi Seieido Corp.), and milled at a maximumspeed for 1 minute to give a PTT composition particle prepolymer. Theprepolymer had a particle size of 1 mm, a particle weight of 0.95mg/particle, a terminal carboxyl group content of 32 meq/kg, and acyclic dimer content of 2.7% by weight.

The prepolymer thus obtained was heated at 200° C. for 15 minutes to becrystallized, and subjected to solid-state polymerization at 205° C. ata vacuum degree of 5 Pa. Table 1 shows the physical properties of thePTT composition particles thus obtained. The PTT composition particlesthus obtained were excellent in whiteness and oxidation resistancestability, and had a decreased cyclic dimer content.

Next, a spinning experiment was carried out in the following manner.

The PTT composition particles obtained in Example 1 or 2 were dried at130° C. to have a moisture content of 50 ppm or less, and melted at 260°C. and extruded with a twin-screw extruder. The extruded yarn was woundat a rate of 1,600 m/min (each package having a weight of 3 kg) to givean undrawn yarn. In addition, the residence time during melting wasabout 10 minutes.

The undrawn yarn thus wound was hot drawn so that the elongation became40% by passing the yarn through hot rolls at 55° C. and a hot plate at140° C. to give a filaments yarn of 84 dtex/36 f. The spinningexperiment was carried out for 3 days, and neither yarn breakage norfluff formation was observed during the winding step and drawing step ofthe undrawn yarn.

EXAMPLE 4 and 5

The procedure of Example 1 was repeated except that the solid-statepolymerization was carried out under conditions explained below.

The PTT composition particle prepolymer was crystallized under thefollowing conditions: the prepolymer was heated at 210° C. for 15minutes by the outer wall of an apparatus while nitrogen gas heated at207° C. was being allowed to flow at a flow rate (superficial velocity)of 100 cm/min in terms of a standard state; the crystallized PTTcomposition particle prepolymer was charged into a solid-statepolymerization apparatus, and heated at 205° C. by the outer wall whilea nitrogen gas heated at 205° C. was being allowed to flow at a flowrate (superficial velocity) of 100 cm/min in terms of a standard stateto effect solid-state polymerization and give PTT composition particles.Table 1 shows a solid-state polymerization time.

The PTT composition particles thus obtained were excellent in whitenessand oxidation resistance stability, and had a decreased cyclic dimercontent.

Next, a spinning experiment was carried out in the following manner.

The PTT composition particles obtained in Example 4 or 5 were dried at130° C. to have a moisture content of 50 ppm or less, and melted at 260°C. and extruded with a twin-screw extruder. The extruded yarn was woundat a rate of 1,600 m/min (each package having a weight of 3 kg) to givean undrawn yarn. The residence time during melting was about 10 minutes.

The undrawn yarn thus wound was hot drawn so that the elongation became40% by passing the yarn through hot rolls at 55° C. and a hot plate at140° C. to give a filaments yarn of 84 dtex/36 f. The spinningexperiment was carried out for 3 days, and neither yarn breakage norfluff formation was observed during the winding step and drawing step ofthe undrawn yarn.

EXAMPLE 6 and 7

Dimethyl terephthalate in an amount of 1,300 g (6.7 moles), 1,144 g (15moles) of PDO and 0.78 g of titanium butoxide were charged into a3-liter autoclave equipped with plate-like blades. A transesterificationreaction was carried out at 220° C. while methanol was being distilledoff. The transesterification reaction ratio was 95%. After finishing thetransesterification reaction, the reaction products thus obtained wereatomized by applying a nitrogen gas pressure of 0.5 MPa, and sprayed togive particles. The particles thus obtained had a particle size of 0.3mm, a particle weight of 0.3 mg/particle, a terminal carboxyl groupcontent of 30 meq/kg, and a cyclic dimer content of 2.7% by weight.

The particles thus obtained were heated from 70° C. to 200° C. in onehour at a vacuum degree of 5 Pa to be crystallized. The molecular weightincreased during heating. The particles were then subjected tosolid-state polymerization at 205° C. at a vacuum degree of 5 Pa to givePTT composition particles. Table 1 shows a solid-state polymerizationtime and the physical properties of the PTT composition particles thusobtained. The PTT composition particles thus obtained were excellent inwhiteness and oxidation resistance stability, and contained cyclic dimerin a decreased amount.

EXAMPLE 8

The procedure of Example 1 was repeated except that terephthalic acidwas used in place of dimethyl terephthalate in the same amount in termsof moles while water was being distilled off.

The granular prepolymer had a particle size of 1.0 mm, a weight of 0.95mg/particle, a terminal carboxyl group content of 34 meq/kg, and acyclic dimer content of 2.6% by weight.

The PTT composition particles thus obtained were excellent in whitenessand oxidation resistance stability, and had a decreased cyclic dimercontent.

EXAMPLE 9

The PTT composition particles obtained in Example 1 were left in a steamatmosphere at 205° C. for 1 hour, and then dried. Although the PTTcomposition particles then showed no significant changes in physicalproperties, they contained cyclic dimer in an amount as small as 1.0% byweight after the melting test at 260° C. Moreover, the PTT compositionparticles were subjected to a light-resistance test with a fadeometer at83° C. for 100 hours, and showed no substantial yellowness.

When the PTT composition particles that were obtained in Example 1 andthat were not treated with steam were subjected to a remelting test at260° C. for 30 minutes, they contained 1.8% by weight of cyclic dimer incontrast to the above results. Moreover, the PTT composition particleswere subjected to a light-resistance test with a fade-ometer at 83° C.for 100 hours, and showed yellowness to a certain degree.

In addition, as a result of subjecting the PTT composition particleshaving been treated with steam to solid-state polymerization at 205° C.for 1 hour at a vacuum degree of 5 Pa, they showed no increase inintrinsic viscosity. The results show that the catalyst is deactivatedby the steam treatment.

EXAMPLE 10

The PTT composition particles obtained in Example 1 were left in 1% byweight of an aqueous phosphoric acid solution at 130° C. for 1 hour, andthen dried. Although the PTT composition particles thus obtained showedno significant changes in physical properties, they contained, after themelting test at 260° C., cyclic dimer in an amount as small as 0.9% byweight. Moreover, the PTT composition particles were subjected to alight-resistance test with a fade-ometer at 83° C. for 100 hours, andshowed no substantial yellowness.

In addition, as a result of subjecting the PTT composition particleshaving been treated with the aqueous phosphoric acid solution tosolid-state polymerization at 205° C. for 1 hour at a vacuum degree of 5Pa, they showed no increase in intrinsic viscosity. The results showthat the catalyst is deactivated by the aqueous phosphoric acid solutiontreatment.

COMPARATIVE EXAMPLE 1

The procedure of Example 1 was repeated except that the meltpolycondensation was carried out at a polycondensation temperature of280° C. The prepolymer pellets thus obtained showed an intrinsicviscosity of 0.7 dl/g, L* of 74 and b* of 7.0, contained 40 meq/kg ofterminal carboxyl groups and 2.9% by weight of cyclic dimer, stronglycolored yellow, and had a dull color tone.

In the same manner as in Example 1, the pellets were ground to giveparticles, and the particles were subjected to solid-statepolymerization. The solid-state polymerization rate was low. Moreover,because the PTT composition particles thus obtained contained terminalcarboxyl groups in a large amount, they were greatly colored, and weredrastically colored during drying heat treatment.

COMPARATIVE EXAMPLE 2

The procedure of Example 1 was repeated except that the prepolymerpellets having a weight of 25 mg/pellet (each pellet having acylindrical form 2.4 mm in diameter and 4.0 mm in height) were subjectedto solid-state polymerization without grinding the pellets. The PTTcomposition particles thus obtained had an intrinsic viscosity of 0.61dl/g.

EXAMPLE 11

The PTT composition particles obtained in Example 3 were dried under anitrogen stream at 130° C. to have a moisture content of 10 ppm. Thedried particles were fed to an extruder, and melted at 290° C. Themolten material was extruded through round-shaped spinning orifices(0.23 mm (in diameter)×2500). No screw pressure variation was observedin the extruder, and spinning was conducted smoothly.

Cold air at 20° C. and a relative humidity of 90% was blown against thefilaments thus extruded, at a speed of 0.4 m/sec so that the filamentswere cooled and solidified. A finishing agent was imparted to thesolidified filaments, and the filaments were wound at a rate of 1,600m/min to give an undrawn yarn. The undrawn yarn thus otained wassubsequently drawn by passing it through hot rolls at 55° C. and a hotplate at 140° C. so that the elongation became about 40%, to give adrawn yarn of 500 dtex/250 f. The drawn yarn thus obtained showed astrength of 5.3 cN/dtex and an elastic modulus of 25 cN/dtex.

Three PTT yarns thus obtained were doubled and twisted with both thefirst and the second twist being at 390 T/m to give a raw cord of 1,500dtex/750 f. The raw cord was coated with an RFL solution containing 20%by weight of a resin. The raw cord was then dried at 130° C. and at 225°C. with a drying machine so that the resin coating ratio became 5% byweight to give a tire cord.

A bias tire was prepared from the tire cord thus obtained, and subjectedto a rotation test.

A 1-ton passenger car was assumed to be driven on an asphalt surface at35° C. at a speed of 200 km/hr, and a rotation test on the tire wasperformed for 96 hours by rotating the tire at the same speed while thesame contact pressure was applied thereto.

After the rotation test for 96 hours, the tire cord was taken out of thetire, and a strength retention ratio was measured. As a result, it wasfound that no substantial lowering of the strength took place.

EXAMPLE 12

The composition particles in Example 1 and the polymer pellets inComparative Example 2 were left in a room for a month. The particles andthe pellets were subjected to a drying test.

When the particles and the pellets were maintained in a dried air at160° C., it took 3 hours until the moisture content of the compositionparticles in Example 1 attained 50 ppm or less, and it took 15 hoursuntil the moisture content of the polymer pellets in Comparative Example2 attained 50 ppm or less. The composition particles in Example 1 thenshowed no change in b*, whereas the polymer pellets in ComparativeExample 2 showed an increase in b* of 0.4.

The composition particles in Example 1 that were dried to have amoisture content of 40 ppm were melted with an extruder and the moltenmaterial could be stably discharged even at 247° C. On the other hand,when the polymer pellets in Comparative Example 2 that were dried tohave a moisture content of 40 ppm were processed in the same manner,they were incompletely melted, and the pressure varied greatly. TABLE 1Amount (%) Solid-state of passed polymerization Particles ParticlesTemp. Time [η] Size Weight 10 500 (° C.) (hr) (dl/g) (mm) (mg/particle)mesh mesh Ex. 1 205 3 0.92 1.0 0.96 96 1 Ex. 2 205 5 1.30 1.0 0.96 95 3Ex. 3 205 10 1.67 1.0 0.96 97 1 Ex. 4 207 3 0.95 1.0 0.96 95 3 Ex. 5 2075 1.32 1.0 0.96 95 2 Ex. 6 205 3 1.05 0.3 0.15 98 2 Ex. 7 205 5 1.40 0.30.15 99 2 Ex. 8 205 3 0.91 1.0 0.96 95 2 Ex. 9 205 3 0.92 1.0 0.95 97 1Ex. 10 205 3 0.93 1.0 0.95 96 2 Comp. 205 3 0.79 1.0 0.94 95 1 Ex. 1Comp. 205 3 0.61 4.0 25.5 1 0 Ex. 2 Terminal carboxyl Cyclic dimerOxidation group content content resistance (meq/kg) (wt. %) L* b*stability Ex. 1 23 0.9 88 1 18 Ex. 2 20 0.8 89 2 19 Ex. 3 20 0.6 90 2 19Ex. 4 15 0.8 89 1 18 Ex. 5 13 0.7 90 2 19 Ex. 6 8 0.6 91 0 15 Ex. 7 90.5 91 0 15 Ex. 8 25 0.7 90 1 19 Ex. 9 22 0.9 89 1 17 Ex. 10 25 0.9 90 116 Comp. Ex. 1 30 2.6 83 7 26 Comp. Ex. 2 25 1.2 88 3 21Industrial Applicability

The PTT composition particles of the present invention are excellent inwhiteness, oxidation resistance stability, moldability and uniformity,and the particle shape is fine and uniform. The PTT compositionparticles therefore show a significant heat transfer effect, and have atleast one of such excellent effects as shortening the drying time andinhibiting thermal deterioration of the particles due to loweredextrusion temperature. Accordingly, when the PTT composition particlesof the invention are used as a raw material, a fiber (spun without yarnbreakage), a film, or the like, of high quality can be produced withhigh productivity.

1. Poly(trimethylene terephthalate) composition particles comprising 80%by weight or more of trimethylene terephthalate units based on theentire repeating units, having an intrinsic viscosity from 0.8 to 2dl/g, and satisfying the following conditions (a) to (c): (a) thecomposition particles have a particle size of 3 mm or less and a weightof less than 1 mg/particle; (b) the composition particles have aterminal carboxyl group content of 25 meq/kg or less; and (c) thecomposition particles have a cyclic dimer content of 1.5% by weight orless.
 2. The poly(trimethylene terephthalate) composition particlesaccording to claim 1, wherein the poly(trimethylene terephthalate)composition particles have a cyclic dimer content of 2% by weight orless after maintaining the particles in a molten state at 260° C. for 30minutes.
 3. The poly(trimethylene terephthalate) composition particlesaccording to claim 1 or 2, wherein 95% or more of the particles passthrough a 10-mesh filter, and 5% or less of the particles pass through a500-mesh filter.
 4. Poly(trimethylene terephthalate) compositionparticles suited to solid-state polymerization, comprising 80% by weightor more of trimethylene terephthalate units based on the entirerepeating units, having an intrinsic viscosity from 0.1 to 0.79 dl/g,and satisfying the following conditions (a) to (c): (a) the compositionparticles have a particle size of 3 mm or less and a weight of less than1 mg/particle; (b) the composition particles have a terminal carboxylgroup content of 35 meq/kg or less; and (c) the composition particleshave a cyclic dimer content from 1.6 to 3.5% by weight.
 5. Thepoly(trimethylene terephthalate) composition particles suited tosolid-state polymerization according to claim 4, wherein 95% or more ofthe particles pass through a 10-mesh filter, and 5% or less of theparticles pass through a 500-mesh filter.
 6. A process for producingpoly(trimethylene terephthalate) composition particles comprising thefollowing steps (1) to (3): (1) a step of reacting terephthalic acidand/or a lower alcohol ester derivative of terephthalic acid with1,3-propanediol to form 1,3-propanediol ester of terephthalic acidand/or a polymer thereof; (2) a step of granulating 1,3-propanediolester of terephthalic acid and/or a polymer thereof obtained in the step(1); and (3) a step of heating granulated 1,3-propnanediol ester ofterephthalic acid and/or a polymer thereof in a solid-state, whereby theintrinsic viscosity is increased by 0.1 dl/g or more.
 7. The process forproducing poly(trimethylene terephthalate) composition particlesaccording to claim 6, wherein the method of granulating 1,3-propanediolester of terephthalic acid and/or a polymer thereof is at least one ofthe following methods (1) to (3): (1) a method comprising extruding theester and/or the polymer in a molten state, and then cutting theextruded material; (2) a method comprising atomizing the ester and/orthe polymer in foggy state, and then finely granulating the atomizedmaterial; and (3) a method comprising solidifying the ester and/or thepolymer, and then crushing the solidified material.
 8. The process forproducing poly(trimethylene terephthalate) composition particlesaccording to claim 6 or 7, wherein the particle size is 3 mm or less,and the particle weight is less than 1 mg/particle.
 9. The process forproducing poly(trimethylene terephthalate) composition particlesaccording to claim 7, wherein 95% or more of the particles pass througha 10-mesh filter, and 5% or less of the particles pass through a500-mesh filter.
 10. The process for producing poly(trimethyleneterephthalate) composition particles according to any one of claims 6 to9, wherein the composition particles have a terminal carboxyl groupcontent originating from the polymer of 1,3-propanediol ester ofterephthalic acid of 35 meq/kg or less.
 11. A process for producingpoly(trimethylene terephthalate) composition particles comprisingheating the poly(trimethylene terephthalate) composition particlesaccording to claim 3 or 4 in a solid state to increase the intrinsicviscosity by 0.1 dl/g or more.
 12. The process for producingpoly(trimethylene terephthalate) composition particles according to anyone of claims 6 to 11, wherein the poly(trimethylene terephthalate)composition particles are heated in a solid state to increase theintrinsic viscosity by 0.1 dl/g or more, and part of or the entire ofthe polycondensation activity remaining in the catalyst is deactivated.13. The process for producing poly(trimethylene terephthalate)composition particles according to claim 12, wherein the method ofdeactivating part of or the entire of the polycondensation activity ofthe catalyst is a method comprising contacting the particles with apolar compound having a temperature of 50° C. or above.
 14. A processfor producing poly(trimethylene terephthalate) composition particlescomprising contacting the poly(trimethylene terephthalate) compositionparticles according to any one of claims 1 to 3 with a polar compoundhaving a temperature of 50° C. or above.
 15. The process for producingpoly(trimethylene terephthalate) composition particles according toclaim 13 or 14, wherein the polar compound is at least one substanceselected from the group consisting of water, methanol, phosphoric acid,hydrogen chloride, sulfuric acid and ammonia.
 16. A molded articleprepared by molding the poly(trimethylene terephthalate) compositionparticles according to any one of claims 1 to
 3. 17. A fiber prepared bymolding the poly(trimethylene terephthalate) composition particlesaccording to any one of claims 1 to
 3. 18. A tire cord prepared bymolding poly(trimethylene terephthalate) composition particlescomprising 80% by weight or more of trimethylene terephthalate unitsbased on the entire repeating units, and having an intrinsic viscosityfrom 0.8 to 2 dl/g.
 19. A tire for which a tire cord according to claim18 is used.